| 1. |
- Ribca, Iuliana, 1993-, et al.
(author)
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Effect of Molecular Organization on the Properties of Fractionated Lignin-Based Thiol-Ene Thermoset Materials
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Other publication (other academic/artistic)abstract
- In this study, the combination of sequential solvent fractionation of technical Kraft lignin were followed by allylation of most OH functionalities to give highly functional thermoset resins. All lignin fractions were highly functionalized on the phenolic (≥95%) and carboxylic acid OH (≥85%), and to a significant extent on the aliphatic OH moieties (between 43 and 75%). The resins were subsequently cross-linked using thiol-ene chemistry. The high amount of allyl functionalities resulted in a high cross-link density. DMA measurements showed that thioether content dominates the performance of these thermosets with a glass transition temperature (Tg) between 73 and 99 °C and with a storage modulus between 1.9 and 3.8 GPa for all thermosets. The lignin fractions and lignin-based thermosets morphology, at nanoscale, was studied by wide angle X-ray scattering measurements (WAXS). Two π-π stacking interactions were observed: sandwich (≈4.1–4.7 Å) and T-shaped (≈5.5–7.2 Å). The introduction of allyl functionalities weakens the T-shaped π-π stacking interactions. A new signal corresponding to a distance of ≈3.5 Å was observed in lignin-based thermosets, which was attributed to a thioether organized structure. At the same time, a lignin superstructure, was observed with a distance/size corresponding to 7.9-17.5 Å in all samples.
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| 2. |
- Ribca, Iuliana, 1993-, et al.
(author)
-
Effect of Molecular Organization on the Properties of Fractionated Lignin-Based Thiol-Ene Thermoset Materials
- 2023
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In: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 8:28, s. 25478-25486
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Journal article (peer-reviewed)abstract
- In this study, the combination of sequential solvent fractionation of technical Kraft lignin was followed by allylation of most OH functionalities to give highly functional thermoset resins. All lignin fractions were highly functionalized on the phenolic (≥95%) and carboxylic acid OH (≥85%) and to a significant extent on the aliphatic OH moieties (between 43 and 75%). The resins were subsequently cross-linked using thiol-ene chemistry. The high amount of allyl functionalities resulted in a high cross-link density. Dynamic mechanical analysis measurements showed that the thioether content, directly related to the allyl content, strongly affects the performance of these thermosets with a glass transition temperature (Tg) between 81 and 95 °C and with a storage modulus between 1.9 and 3.8 GPa for all thermosets. The lignin fractions and lignin-based thermosets’ morphology, at the nanoscale, was studied by wide-angle X-ray scattering measurements. Two π-π stacking interactions were observed: sandwich (≈4.1-4.7 Å) and T-shaped (≈5.5-7.2 Å). The introduction of allyl functionalities weakens the T-shaped π-π stacking interactions. A new signal corresponding to a distance of ≈3.5 Å was observed in lignin-based thermosets, which was attributed to a thioether organized structure. At the same time, a lignin superstructure was observed with a distance/size corresponding to 7.9-17.5 Å in all samples.
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| 3. |
- Ribca, Iuliana, 1993-, et al.
(author)
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Exploring the Effects of Different Cross-Linkers on Lignin-Based Thermoset Properties and Morphologies
- 2021
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In: ACS Sustainable Chemistry and Engineering. - : American Chemical Society (ACS). - 2168-0485. ; 9:4, s. 1692-1702
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Journal article (peer-reviewed)abstract
- The search for sustainable material solutions has put lignin as one of the prime candidates for aromatic building blocks in macromolecular materials. The present study aimed to demonstrate how lignin-based thermoset resins can be utilized in combination with different cross-linkers. Kraft lignin was used to produce thermosets with tunable mechanical and morphological properties. The lignin-based thermosets were obtained via a thermally induced thiol–ene reaction. The first part of this work was focused on Kraft lignin solvent fractionation and chemical modification of the ethanol soluble fraction. Chemical analysis indicated that the allylation process was selective toward phenolic hydroxyl groups. SAXS and SEM studies demonstrated that solvent fractionation and allylation processes affected the molecular and nanoscale morphological characteristics of lignin. The second part’s focus was on how the properties of thermosets can be tuned by using three different cross-linkers. The dynamic mechanical and morphological properties of three different thermosets were investigated via DMA, SAXS, and WAXS techniques. The three different thermosets exhibit similar molecular morphology but different storage modulus and glass transition temperature. In this work, it was shown that despite lignin’s heterogeneity it was possible to produce thermosetting materials with tunable properties.
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| 4. |
- Ribca, Iuliana, 1993-, et al.
(author)
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Impact of lignin source on the performance of thermoset resins
- 2023
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In: European Polymer Journal. - : Elsevier BV. - 0014-3057 .- 1873-1945. ; 194, s. 112141-112141
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Journal article (peer-reviewed)abstract
- A series of different technical hardwood lignin-based resins have been successfully synthesized, characterized, and utilised to produce thiol-ene thermoset polymers. Firstly, technical lignin was fractionated and allylated, whereafter it was crosslinked with a trifunctional thiol. Structural and morphological characteristics of the lignin fractions were studied by 1H NMR, 31P NMR, SEC, FTIR, DSC, TGA, and WAXS. The hardwood lignin fractions have a high content of C5-substituted OH groups. The WAXS studies on lignin fractions revealed the presence of two π-π stacking conformations, sandwiched (4.08–4.25 Å) and T-shaped (6.52–6.91 Å). The presence of lignin superstructures with distances/sizes between 10.5 and 12.8 Å was also identified. The curing reaction of the thermosets was investigated by RT-FTIR. Almost all thermosets (excepting one fraction) reached 95% of the thiol conversion in less than 17 h, revealing the enhanced reactivity of the allylated hardwood lignin samples.The mechanical properties of the thermosets were investigated by DMA. The curing performance, as well as the final thermoset properties, have been correlated to variations in chemical composition and morphological differences of lignin fractions. The described results clearly demonstrate that technical hardwood lignins can be utilized for these applications, but also that significant differences compared to softwood lignins have to be considered for material design.
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| 5. |
- Ribca, Iuliana, 1993-
(author)
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Lignin-Based Thermosets with Tunable Mechanical and Morphological Properties : A Study of Structure-Property Relationships
- 2023
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Doctoral thesis (other academic/artistic)abstract
- Nowadays, there is an urgent need to decrease our dependence on fossilresources and shift towards the use of renewable resources for advancingsustainable development. Utilizing renewable and bio-based raw materials,such as lignocellulosic biomass, for designing new materials is a promisingapproach to promote this objective. The main components of lignocellulosicbiomass are cellulose, hemicellulose, and lignin. Lignin is the most abundantaromatic biopolymer in nature and it is produced on a large scale fromchemical pulping processes as technical lignin. Lignin has the potential as asustainable and renewable alternative to fossil-based aromatics in variousapplications, e.g. thermosetting resins.Technical lignin has a complex and heterogeneous structure, with arelatively low chemical reactivity. It is characterized by a high dispersity, thepresence of various functional groups that are unevenly distributed along thelignin chains, and various interunit linkages between the monoaromatics. Toovercome the challenges associated with lignin heterogeneity, technicallignin can be fractionated and/or chemically modified.In this work, LignoBoost Kraft lignin was used as a starting material toproduce lignin-based thiol-ene thermosets. Firstly, lignin was fractionatedusing two approaches: 1) sequential solvent fractionation, and 2) microwaveassistedextraction. These fractionation approaches enabled access to ligninfractions with unique and tunable properties. Subsequently, lignin waschemically modified, in particular through allylation. Two allylation reagentswere used: allyl chloride and diallyl carbonate. The use of allyl chlorideenables a selective allylation of the phenolic OH groups, leaving the aliphaticand carboxylic acid OH groups unmodified. On the other hand, diallylcarbonate can react with all the aforementioned OH groups, leading to ahigher degree of allylation. Subsequently, allylated lignin was thermallycross-linked with various polyfunctional thiols, leading to thiol-enethermosets. The structure-property relationships of the thermosets wereinvestigated by varying several parameters, including the lignin source,fractionation approach, chemical modification, and thiol cross-linker. Byadjusting these parameters, various thermosets with tunable mechanical andmorphological properties were produced. Understanding the structurepropertyrelationships of these bio-based materials is crucial for identifyingpotential applications.
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| 6. |
- Truncali, Alessio, et al.
(author)
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Microwave-assisted fractionation and functionalization of technical lignin toward thermoset resins
- 2023
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In: Journal of Applied Polymer Science. - : Wiley. - 0021-8995 .- 1097-4628. ; 140:45
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Journal article (peer-reviewed)abstract
- Lignin is the most abundant aromatic biopolymer, with a potential to serve as a building block of rigid and thermally stable bio-based materials. However, it is still underutilized because of the heterogeneous and not fully understood chemical structure. Here, technical softwood Kraft lignin is refined in to narrow-dispersity and relatively low molar mass fractions by microwave-assisted processing, followed by microwave-assisted allylation and further application in lignin-based thermosets. This microwave processing is carried out under non-catalyzed conditions using a low boiling point solvent and elevated pressure. The properties of the retrieved fractions are investigated by 31P-NMR, heteronuclear single quantum coherence spectroscopy-NMR, SEC, differential scanning calorimetry, and thermogravimetric analysis. The extraction yield of the selected lignin fraction is around 25%, with the number-average molar mass (Mn), weight-average molar mass (Mw), and dispersity (Đ) significantly reduced. The chemically modified lignin is characterized by 31P NMR and FTIR, which provides evidence of the introduction of the allyl moieties. The analyses demonstrate that 90 ± 3% of the hydroxyl groups in fractionated lignin are successfully allylated. Subsequently, the allylated lignin is cross-linked through thermally induced thiol-ene chemistry to produce lignin-based thermosets. The final thermosets exhibit a storage modulus of 4050 ± 60 MPa and a Tg of 105 ± 5°C.
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| 7. |
- Truncali, Alessio, et al.
(author)
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Microwave-Assisted Fractionation and Functionalization of Technical Lignin Towards Thermoset Resins
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Other publication (other academic/artistic)abstract
- Lignin is the main source of aromatic natural polymers, with a potential to serve as a building block of rigid and thermally stable bio-based materials. However, because of its heterogeneity differences and not fully understood chemical structure it is still underutilized. Therefore, in this paper, technical softwood Kraft lignin is refined in to narrow-dispersity and relatively low molecular weight fractions by microwave-assisted processing. This process was carried out under non-catalytic conditions using a low boiling point solvent and higher pressure. The chemical properties of the retrieved fractions were investigated by 31P NMR, HSQC NMR, SEC, DSC, and TGA. One of the retrieved soluble lignin fractions was successfully chemically modified by microwave processing. The chemically modified lignin was characterized by 31P NMR and FTIR, which provided evidence of the introduction of the allyl moieties. Subsequently, the allylated lignin was cross-linked through thermally induced thiol-ene chemistry to produce lignin-based thermosets.
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| 8. |
- Wolfs, Jonas, et al.
(author)
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Polythionourethane Thermoset Synthesis via Activation of Elemental Sulfur in an Efficient Multicomponent Reaction Approach
- 2023
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In: ACS Sustainable Chemistry and Engineering. - : American Chemical Society. - 2168-0485. ; 11:9, s. 3952-3962
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Journal article (peer-reviewed)abstract
- For the transition toward a safer and more sustainable production of polymeric materials, new synthetic concepts need to be developed. Herein, we describe a catalytic, solvent-free synthesis approach for novel thionourethane thermoset materials, in which the diisothiocyanate reactant is generated in situ via a sulfurization of isocyanides with elemental sulfur, preventing the exposure and handling of the diisothiocyanate. In this one-pot procedure, castor oil fulfills a dual role: (i) acting as the solvent for the in situ diisothiocyanate synthesis in the first step and (ii) reacting as the polyol component in the subsequent thionourethane thermoset formation. The kinetics of the consecutive two steps were studied in detail via real-time IR measurements, and the thermoset crosslinking step was found to be thermally triggerable after the diisothiocyanate reactant is quantitatively formed, enabling high control over the curing process of the system. Differential scanning calorimetry, thermogravimetric analysis, and rheological measurements were performed to investigate the thermal and mechanical properties of the novel thionourethane thermosets and then compared to analogous polyurethane materials. Our results demonstrate an unprecedented approach for thermoset synthesis via an in situ reagent synthesis, i.e., the generation of isothiocyanates from isocyanides by catalytic activation of elemental sulfur, and subsequent thermally triggerable thermosetting with a polyol, resulting in materials with appealing properties.
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| 9. |
- Zhang, Qilun, 1992-, et al.
(author)
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Industrial Kraft Lignin Based Binary Cathode Interface Layer Enables Enhanced Stability in High Efficiency Organic Solar Cells
- 2023
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In: Advanced Materials. - : WILEY-V C H VERLAG GMBH. - 0935-9648 .- 1521-4095.
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Journal article (peer-reviewed)abstract
- Herein, a binary cathode interface layer (CIL) strategy based on the industrial solvent fractionated LignoBoost kraft lignin (KL) is adopted for fabrication of organic solar cells (OSCs). The uniformly distributed phenol moieties in KL enable it to easily form hydrogen bonds with commonly used CIL materials, i.e., bathocuproine (BCP) and PFN-Br, resulting in binary CILs with tunable work function (WF). This work shows that the binary CILs work well in OSCs with large KL ratio compatibility, exhibiting equivalent or even higher efficiency to the traditional CILs in state of art OSCs. In addition, the combination of KL and BCP significantly enhanced OSC stability, owing to KL blocking the reaction between BCP and nonfullerene acceptors (NFAs). This work provides a simple and effective way to achieve high-efficient OSCs with better stability and sustainability by using wood-based materials. This work introduces industrial solvent fractionated LignoBoost kraft lignin (KL) in highly efficient organic solar cells (OSCs) by binary cathode interface layer (CIL) strategy, which can significantly improve the stability of both binary and ternary photoactive layer (PAL) OSC, owing to the passivation of diffusion and reaction between bathocuproine (BCP) and nonfullerene acceptors (NFAs). The results combine sustainable wood-based material with classic interface materials in advance NFA-OSCs.image
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